DE10245703A1 - Process for the preparation of polyisocyanates of the diphenylmethane series by phosgenation of unneutralized polyamine of the diphenylmethane series - Google Patents

Abstract

Production of diphenylmethane polyisocyanates involves (1) reacting aniline and formaldehyde in presence of HCl to give a mixture containing diphenylmethane polyamines, HCl, aniline and water; (2) distilling off the excess of aniline and water to give a product containing aniline at a maximum of 10 wt.% based on the polyamines and water and a maximum of 5 wt.% based on the polyamines; and (3) phosgenating the product.

Description

The invention relates to a method for the production of polyisocyanates of the diphenylmethane series, which by reacting the corresponding polyamines of the diphenylmethane series can be obtained with phosgene.

Polyisocyanates of the diphenylmethane series are understood to mean isocyanates and isocyanate mixtures of the following types:

Analogously, polyamines of the diphenylmethane series are understood to mean compounds and compound mixtures of the following type:

Large-scale production of Isocyanates by reacting amines with phosgene in solvents is known and described in detail in the literature (Ullmanns encyclopedia der Technische Chemie, 4th edition, volume 13, page 347-357, publisher Chemie GmbH, Weinheim, 1977). Based on this procedure, the Polyisocyanate mixture produced that as a polyisocyanate component in the production of polyurethane foams and others using the polyaddition process produced polyurethane plastics is used.

The continuous, discontinuous or semi-continuous production of polyamines from the diphenylmethane series, hereinafter also referred to as MDA, is in numerous patents and publications. Usually it is produced by reacting aniline and formaldehyde in the presence of acidic catalysts. HCl is usually considered to be more acidic Catalyst used. The acid catalyst is according to the state the technology at the end of the process before the final processing steps (such as the removal of excess aniline by distillation) neutralized by adding a base and thus consumed.

Main products of acid catalyzed Reaction of aniline and formaldehyde are the diamine 4,4'-MDA, its positional isomers 2,4'-MDA and 2,2'-MDA as well as higher homologues Diphenylmethane series polyamines. The polyisocyanates of the diphenylmethane series, hereinafter referred to as MDI, are by phosgenation of the corresponding Made polyamines. The diphenylmethane series polyisocyanates thus produced contain the various isocyanate isomers and their higher homologs in the same composition as the polyamines from which they are made were manufactured. Control variable to influence the Isomer distribution is that in the acid catalyzed reaction of Aniline and formaldehyde amount of acid used in the process Catalyst. To MDI with the desired To be able to produce isomer distribution must therefore be considerable in some cases Amounts of acid catalyst and correspondingly significant amounts at base for the neutralization of the acid catalyst can be used. from that there are still larger quantities on saline wastewater flows and accordingly a high reprocessing and disposal effort.

It has been a long time since methods to circumvent or alleviate this problem have been found Time the goal of numerous experiments and works that are described in the literature. For example, WO-A1-0174755 describes the production of polyamines from the diphenylmethane series in the presence of heterogeneous catalysts which take over the function of the acid catalyst. In contrast to the homogeneous catalysts usually used, this type of catalyst can simply be separated from the reaction mixture and accordingly does not have to be neutralized before working up. However, a disadvantage of this process is that the acidic solid deactivates over time and that the range of products accessible via these catalysts is restricted. EP-A1-1167343 describes the MDA production according to the prior art, expanded by an additional separation of the 2,4'-MDA and 2,2'-MDA isomers, and their reaction with formaldehyde and returning this mixture to the beginning of the process , The recycled isomers are thus preferably converted to higher molecular weight MDA components. As a result, the close coupling of catalyst use and formation of 2,4'- and 2,2'-MDA is alleviated by introducing a further control variable. However, a disadvantage of this process is that the conversion of the recycled isomers to higher MDA homologues can have a negative effect on the product properties of the MDI produced by subsequent phosgenation, and that additional apparatus expenditure for the distillation is required for the isomer separation.

Object of the present invention it was therefore a technical process for the production of polyisocyanates the diphenylmethane series with which the consumption on acid catalyst and correspondingly from base for neutralization of the acidic catalyst reduced or avoided at the MDA level can be.

The object is achieved by a process for the preparation of polyisocyanates of the diphenylmethane series, where you

• a) aniline and formaldehyde in the presence of HCl to a product mixture containing polyamines from the diphenylmethane series, HCI, aniline and water reacted, and afterwards
• b) excess aniline and water is removed by distillation to give a product mixture containing polyamines from the diphenylmethane series, HC1 and aniline a salary of at most 10 wt .-% based on the polyamines and water with a content of at most 5 wt .-% based on the polyamines, and then
• c) the product mixture containing polyamines from the diphenylmethane series, HCl and aniline with a content of at most 10 wt .-% based on the polyamines and water with a content of at most 5 wt .-% based on the polyamines phosgenated.

The process can be continuous, be carried out discontinuously or semi-continuously. With the procedure you can Diphenylmethane series polyisocyanates without neutralization of the acid HCl catalyst can be produced at the stage of MDA production.

The polyamine or polyamine mixture of the diphenylmethane series produced by the process in step a) is obtained by condensation of aniline and formaldehyde in the presence of the acid catalyst (HJ Twitchett, Chem. Soc. Rev. 3 (2), 209 (1974), MV Moore in:.... Kirk-Othmer encycl Chem Technol, 3 ^rd Ed, New York, 2, 338-348 (1978)).. It is irrelevant for the process according to the invention whether aniline and formaldehyde are first mixed in the absence of HCl and then HCl is added, or whether a mixture of aniline and HCl is reacted with formaldehyde.

Suitable polyamine mixtures of the diphenylmethane series are common obtained by condensation of aniline and formaldehyde in the molar Stoffinengenverhältnis 20: 1 to 1.6: 1, preferably 10: 1 to 1.8: 1 and a molar molar ratio of Aniline and HCl from 50: 1 to 1: 1, preferably 20: 1 to 2: 1.

Technically, formaldehyde becomes common as watery solution used. It can however also other methylene group-providing compounds such as e.g. Polyoxymethylene glycol, para-formaldehyde or trioxane are used become.

As acidic catalysts for MDA production strong organic and preferably inorganic acids have proven their worth. For the method according to the invention HCl is the only acid catalyst, preferably in the form the watery Solution, suitable.

In a preferred embodiment of the process, aniline and HCl are first combined. This mixture in a further step, if necessary after removal of heat with formaldehyde at temperatures between 20 ° C and 100 ° C, preferably at 30 ° C to 70 ° C suitable Way mixed and then subjected to a preliminary reaction in a suitable residence apparatus. The prereaction takes place at temperatures between 20 ° C. to 100 ° C., preferably in the temperature range 30 ° C up to 80 ° C. Following mixing and pre-reaction, the temperature of the reaction mixture in stages or continuously and optionally under pressure to 100 ° C up to 250 ° C, preferably to 100 ° C up to 180 ° C, particularly preferably to 100 ° C up to 160 ° C brought.

However, it is also possible to use aniline and formaldehyde first in the absence of HCl in the temperature range from 5 ° C to 130 ° C, preferred of 40 ° C up to 110 ° C, particularly preferably from 60 ° C. up to 100 ° C, to mix and thus react. Here form Condensation products from aniline and formaldehyde (so-called aminal). Following the formation of aminal, there may be present in the reaction mixture Water by phase separation or other suitable process steps, for example, by distillation. The condensation product is then suitable in a further process step with HCl Mixed and preferred in a residence apparatus at 20 ° C to 100 ° C. 30 ° C to 80 ° C one Subjected to pre-reaction. Then the temperature of the Reaction mixture in stages or continuously and if necessary under excess pressure to 100 ° C up to 250 ° C, preferably to 100 ° C up to 180 ° C, particularly preferably to 100 ° C up to 160 ° C brought.

The implementation of aniline and formaldehyde in the presence of HCl to polyamines of the diphenylmethane series in the presence of other substances (e.g. solvents, salts, organic and inorganic acids) happen.

The product mixture obtained in step a) contains next to the one you want MDA still used in excess Aniline, water, HCl as a catalyst and optionally others Substances that have been added to the process. Before implementing this Mix to the corresponding MDI using phosgenation must be the mixture the excess aniline and the water is largely removed. Aniline levels are required of at most 10% by weight, preferably at most 2 wt .-%, particularly preferably based on at most 0.2 wt .-% on the polyamines and water contents of at most 5 wt .-%, preferred of at most 1 wt .-%, particularly preferably based on at most 0.1 wt .-% be adjusted to the polyamines.

Aniline must match the one obtained in step a) Product mixture are largely removed before phosgenation, since aniline would be converted to phenyl isocyanate during phosgenation. phenyl isocyanate is in MDI due to its chain-breaking monofunctionality but undesirable.

Water removal is required because water present in phosgenation with both phosgene as well as with the products and intermediates of phosgenation would respond and thus a reduced yield and undesirable by-products in the MDI would result.

The removal of aniline in step b) succeeds by distillation, although the aniline by reaction is at least partially protonated with HCl. Preferably Water, which is present in the reaction mixture anyway and also must be removed as an entrainer for the removal of the aniline used. But it is also possible use other organic or inorganic entraining agents. For example Is it possible, the solvent as an entrainer to be used, which is also used in phosgenation.

The separation of aniline and water is advantageously carried out in such a way that the acidic reaction mixture the aniline / formaldehyde condensation is fed to a distillation column. The mixture of aniline and water and possibly additional The entrainer is used as a low boiler fraction at the top of the column decreased. The aniline may optionally be worked up (for example by phase separation) in MDA production. The one remaining in the swamp The product mixture is largely aniline and water-free and contains aniline with contents of at most 10.0% by weight based on the polyamines and water contained Held by at most 5.0% by weight based on the polyamines contained. To the ones you want Setting low aniline levels can be an additional Addition of water and / or other entrainer may be necessary. This can e.g. by doing that in the distillation stage incoming material a corresponding amount of water and / or amount of solvent supplied becomes. But it is also possible the required amount of water or solvent vaporous in the distillation stage and thus the for the Distillation necessary Enter energy.

It is also possible that Separation of aniline and water in several stages, preferably in two stages. there can initially the aniline is separated off by distillation with water as entrainer and then water separation in a second distillation stage be carried out using another entrainer.

Aniline contents of at most 10% by weight, preferably at most 2 wt .-%, particularly preferably based on at most 0.2 wt .-% on the polyamines and water contents of at most 5 wt .-%, preferred of at most 1 wt .-%, particularly preferably based on at most 0.1 wt .-% be adjusted to the polyamines.

The product mixture obtained in this way contains polyamines from the diphenylmethane series and HCl as main components and, if appropriate, residual levels of aniline and water, some of the polyamines and possibly aniline being present in protonated form. Nevertheless, this product mixture can then be reacted with phosgene in an inert organic solvent to give the corresponding isocyanates. The molar ratio of polyamine to phosgene is expediently such that 1 to 10 mol, preferably 1.2 to 6 mol, of phosgene are used per mol of amine function in the polyamine. Chlorinated, aromatic hydrocarbons such as monochlorobenzene, dichlorobenzenes, tri have been found as inert solvents for the phosgenation step chlorobenzenes, the corresponding (possibly chlorinated) toluenes and xylenes and chloroethylbenzene have proven successful. In particular, monochlorobenzene, dichlorobenzene or mixtures of these chlorobenzenes are used as inert organic solvents. The amount of solvent is preferably such that the reaction mixture has an MDI content of 2 to 50% by weight, preferably between 5 and 30% by weight, based on the total weight of the reaction mixture. After the reaction of amine and phosgene has ended, excess phosgene, inert organic solvents and HCl are separated off from the reaction mixture. The separated HCl is composed of the HCl formed in the phosgenation of MDA with phosgene and the HCl used as a catalyst for the reaction of aniline with formaldehyde to MDA. The product obtained is MDI, which can be subjected to further processing steps.

The method according to the invention has the advantage that it depends on the use of a base such as NaOH to neutralize the HCl can be used. As a result, saline wastewater flows and thus associated reprocessing and disposal costs avoided. The in the condensation of aniline and formaldehyde as a catalyst HCl used is recovered as a valuable substance during phosgenation and can be returned to the MDA process after appropriate processing. You can also go for a neutralization and washing step in the MDA process to be dispensed with.

example

513 g of aniline were added at 80 ° C within of 20 minutes at the same time 884 g of aniline and 486 g of a 32% aqueous solution formaldehyde solution dripped. After the addition, the mixture was stirred for a further 10 min and then phase separation at 70-80 ° C performed. The amount of the organic phase was 356 g to 35 ° C tempered and then at this temperature within 30 min with the remaining organic phase and 427 g of a 32% aqueous hydrochloric acid added. When the addition is complete and the mixture has been stirred for a further 30 minutes at this temperature was during 10 min at 60 ° C heated and held at this temperature for 30 min. Then was to reflux temperature within 30 min heated and refluxed for 10 h touched.

1177 g of the acidic condensation mixture produced were transferred to a discontinuous distillation apparatus and by blowing water vapor into the sump to an aniline content brought in the bottom of less than 0.1 wt .-% based on polyamine. The largely aniline-free but still water- and HCl-containing Bottom mixture was so long in a second distillation apparatus continuously mixed with chlorobenzene and kept under boiling, until the water content in the sump is below 0.1% by weight, based on polyamine fell. The condensing mixture of chlorobenzene and water can be separated by phase separation to remove the chlorobenzene attributed to the distillation.

Now as a suspension in chlorobenzene existing, largely aniline and water-free acidic rearrangement mixture the aniline / formaldehyde condensation was removed from the distillation apparatus taken. Subsequently chlorobenzene was added and the polyamine content was 16% by weight based on the suspension.

300 of this suspension were g to 55 ° C heated and quickly and with intensive stirring to one at 0 ° C tempered solution of 105 g of phosgene in 310 ml of chlorobenzene. The resulting Reaction mixture was carried out while passing phosgene within 45 min at 100 ° C and subsequently while 10 minutes to reflux temperature heated. After a further 10 min at this temperature, the chlorobenzene distilled off under reduced pressure to a bottom temperature of 100 ° C. The clear crude isocyanate was then in a distillation apparatus at a pressure of 4-6 mbar through a heating bath heated to 260 ° C until the beginning Product transition heated and then cooled to room temperature within 5 min.

The MDI obtained has an NCO content of 32.5% by weight based on MDI.

Claims (5)

Process for the preparation of polyisocyanates the diphenylmethane series, in which one a) Aniline and formaldehyde in the presence of HCl to a product mixture containing polyamines the diphenylmethane series, HCl, aniline and water, and afterwards b) excess aniline and water is removed by distillation to give a product mixture containing polyamines from the diphenylmethane series, HCl and aniline a salary of at most 10 wt .-% based on the polyamines and water with a content of at most 5 wt .-% based on the polyamines, and then c) that Product mixture containing polyamines from the diphenylmethane series, HCl and aniline with a content of at most 10% by weight based on the polyamines and water with a content of at most 5 wt .-% based on the polyamines phosgenated. Process according to claim 1, in which the distillation in the presence of an entrainer. Process according to claim 1, in which the distillation carried out in two stages, where in a first distillation stage aniline in the presence removed from water as entrainer and in a second distillation stage Water removed. Method according to one of claims 1 to 3, in which one in Step b) a product mixture containing polyamines from the diphenylmethane series, HCl and aniline with contents of at most 2% by weight based on the polyamines and water with a content of at most 1 wt .-% based on receives the polyamines and then phosgenated in step c). Method according to one of claims 1 to 4, in which one in Step b) a product mixture containing polyamines from the diphenylmethane series, HCl and aniline with a content of at most 0.2% by weight on the polyamines and water with a maximum content 0.1% by weight, based on the polyamines, and then in step c) phosgenating.